Keith, have you taken it apart to see if there is anything obviously wrong with it? If you know anyone who messes with electronics, it might be worth taking it to them. It might be a cheap fix.
I have 2 older Sears units, one a standard, one a dial-back, and they both have always worked ok for me. I think it's the newer electronics that are used in them that don't play so well with MSD stuff. Never had any issue with the older ones.